A high-strength and stable sealing material for solid oxide fuel cells and its application

Abstract

The present invention relates to a high-strength and stable sealing material for solid oxide fuel cells and its application. The high-strength and stable sealing material for solid oxide fuel cells includes: glass powder modified by surface polysilazane and ceramic powder modified by surface polysilazane; the content of the ceramic powder modified by surface polysilazane is 5-30 wt%; the content of the glass powder modified by surface polysilazane is ≥70 wt%.

Description

Technical Field

[0001] The present invention relates to a high-strength and stable sealing material for solid oxide fuel cells, which is particularly suitable for the connection and sealing between battery components and stainless steel connectors in SOFC stacks. At the same time, it is also applicable to the sealing of stainless steel / high-temperature alloy for metal packaging shells and connectors used in aerospace, communication electronics, etc., belonging to the field of special glass sealing materials. Background Art

[0002] Due to advantages such as high power density, large output power, simple production process, easy assembly, and low cost, the planar solid oxide fuel cell (Planar Solid Oxide Fuel Cell, Planar - SOFC) has become the research focus and key point of technological breakthrough in the field of solid oxide fuel cells. The Planar - SOFC stack consists of a single - cell functional component sintered from yttria - stabilized zirconia oxygen ceramic material (abbreviated as YSZ) electrolyte, Co - based ceramic material cathode with a layered perovskite structure, and Ni - based - YSZ ceramic material anode, as well as two auxiliary parts: stainless steel metal connectors (such as SUS 430, SUS 304, Crofer 22 APU, etc.) and a sealing material. However, fuel gas and air pass through both sides of the planar SOFC respectively, and it is necessary to separate the fuel gas and air at the battery edge through the sealing material in a temperature environment of 600 - 800°C. The environment of long - term high temperature (~40000h), strong air flow impact, and frequent thermal cycling (thousands of times) is a strict test for the sealing material.

[0003] Currently, rigid sealing achieved by the viscous flow of glass or glass - ceramic materials at high temperature is a more stable and more suitable sealing method for Planar - SOFC. During the multi - field operation process in the Planar - SOFC stack, under the combined action of coupling stress and thermal aging, the failure of the sealing glass material includes brittle cracking of the glass material and delamination cracking at the sealing interface. The glass - based sealing ring must have a certain thickness (0.5 - 3 mm) to achieve a certain strength to ensure that the glass sealing ring can be used for processing and battery assembly. However, during the temperature change process from the high working temperature to room temperature, this relatively thick sealing material has a large deformation due to temperature change, and this large deformation easily causes the glass sealing ring to break and thus leads to the sealing failure of the sealing ring. Therefore, improving the mechanical properties of the sealing material, such as tensile strength and compressive strength, will significantly improve the stability and durability of SOFC sealing.

[0004] The properties such as the thermal expansion coefficient and mechanical strength of glass can be improved by preparing glass-based composite sealing materials through compounding with ceramic powders or fibers. Chinese Invention Patent 1 (Application No. 201210257795.5) discloses a glass-ceramic composite sealing material with low boron and no Ba that does not crystallize within the working temperature range. The glass phase plays a sealing role, and the ceramic phase can improve the mechanical strength and expansion coefficient of the sealing material, enhancing the compatibility between the sealing material and battery components. For example, Chinese Invention Patent 2 (EP-A-1010675) discloses the preparation of a composite sealing material of glass powder and filler applicable to solid oxide fuel cells. The filler can increase the low-expansion glass powder from 7.5 to the range of (9 - 13). Taniguchi S et al. in Japan (JOURNAL OF POWER SOURCES, doi.org / 10.1016 / S0378-7753(00)00405-5) added SiO2-Al2O3 ceramic fibers to SiO2-BaO-B2O3-Al2O3 glass to prepare a ceramic fiber / glass composite sealing material, which alleviated the thermal stress generated during battery operation, improving the thermal cycling and sealing airtightness of the battery. However, the above patents did not conduct relevant research and suppression on the chemical interface stability between the glass phase and the ceramic phase during the long-term operation of the sealing material in the stack at 600 - 900°C. For example, Brochu et al. (Journal of the European Ceramic Society, doi:10.1016 / j.jeurceramsoc.2005.08.002) found that new low-expansion phases of SrZrO3 and BaZrO3 (7.9 ppm / °C) would be produced in the composite sealing of B2O3-Al2O3-MgO-CaO-BaO-SrO glass and Y2O3-stabilized ZrO2, resulting in a decrease in the overall CTE. For example, Chinese Invention Patent 3 (Application No. 2021111298078.2) discloses a high-strength sealing material with a bionic structure for medium and high-temperature solid oxide fuel cells. As the holding time at 750°C increased, the plate-like alumina reacted with the glass matrix, resulting in the appearance of BaAl2O4, leading to a decrease in the thermal expansion coefficient and mechanical properties. The research on the thermal physical properties, mechanical properties, chemical stability, and thermal stability of existing sealing glass materials in the free state has reached its limit. How to further improve the sealing stability and durability of Planar-SOFC is a problem faced by this field. Summary of the Invention

[0005] In view of the above-mentioned problems, the present invention proposes a completely new design of composite sealing materials, and specifically provides a high-strength and stable sealing material for solid oxide fuel cells, its preparation method, and applications.

[0006] In a first aspect, the present invention provides a high-strength and stable sealing material for a solid oxide fuel cell, comprising: glass powder modified with polysilazane on the surface and ceramic powder modified with polysilazane on the surface; the content of the ceramic powder modified with polysilazane on the surface is 5-30 wt%; the content of the glass powder modified with polysilazane on the surface is ≥70 wt%. Preferably, the surface modification is carried out by the polysilazane method.

[0007] In the art, the research on the thermal properties, mechanical properties, chemical stability and thermal stability of sealing glass materials in the free state has reached an extreme, but those skilled in the art have ignored the internal microcrack propagation process and inhibition mechanism under the coupled stress field. As a typical brittle material, the present inventor has, for the first time, improved the long-term interfacial chemical stability of the composite sealing material by designing a surface modification layer, thereby improving the sealing stability and durability of Planar-SOFC.

[0008] Specifically, the present disclosure uses amorphous coating on the surfaces of the sealing glass powder and ceramic powder in the high-strength and stable sealing material to improve the interfacial stability, mechanical properties (bending strength, elastic modulus, fracture toughness, etc.) and thermal stability (high thermal conductivity, high expansion) of the sealing material during long-term operation at high temperatures.

[0009] Preferably, the mass of polysilazane in the glass powder modified with polysilazane on the surface is 1-4 wt% of the mass of the glass powder.

[0010] Preferably, the mass of polysilazane in the ceramic powder modified with polysilazane on the surface is 2-10 wt% of the mass of the ceramic powder, preferably 2-8 wt%. Among them, the surface modification is that polysilazane can be cured on the surfaces of the glass powder and ceramic powder at low temperature and can decompose to form a dense amorphous layer at high temperature.

[0011] Preferably, the composition of the glass powder includes: 25-50 moL% of glass network formers, 40-65 moL% of glass network modifiers, 2-10 moL of glass network intermediates, 0-5 moL% of additives, and the sum of the mass percentages is 100 moL%; the particle size D 50 = 1 μm to 10 μm.

[0012] Preferably, the glass network formers contain >25 moL% of SiO2 and less than 10 moL% of B2O3;

[0013] The network modifiers contain >30 moL% of alkaline earth metal oxides RO and <5 moL% of rare earth oxides Re2O3, where R = at least one of Mg, Ca, Ba, Sr;

[0014] The intermediate oxide of the glass network is Ga2O3 or Al2O3;

[0015] The additive is at least one of ZnO, Y2O3, ZrO2, iron oxide, cobalt oxide, and nickel oxide. Preferably, the composition of the glass powder includes: SiO2: 30 - 55 mol%, B2O3: 0 - 10 mol%, sum of RO: 35 - 60 mol%, Al2O3: 1 - 10 mol%, Ln2O3: 1 - 10 mol%, iron oxide: 0 - 3 mol%, cobalt oxide: 0 - 3 mol%, nickel oxide: 0 - 3 mol%, ZnO: 0 - 5 mol%, Y2O3: 0 - 5 mol%, ZrO2: 0 - 5 mol%.

[0016] Preferably, in the alkaline earth metal oxide RO of the network modifier, CaO and SrO are used as regulators for controlling the thermal expansion coefficient of the glass, and the total content of CaO + SrO is < 10 moL%;

[0017] In the alkaline earth metal oxide RO of the network modifier, BaO and MgO are used as precipitants for controlling the precipitation of high-expansion crystal phases SiO2 - BaO and SiO2 - MgO, and the total content of BaO + MgO is ≥ 30 moL%.

[0018] Preferably, the high-expansion phases precipitated in the glass powder include Ba2SiO4, BaSiO3, BaSi2O5, MgSiO3, Mg2SiO4.

[0019] Preferably, the ceramic powder is a ceramic powder with a medium to high thermal expansion coefficient, and is preferably at least one selected from Al2O3, ZrO2, MgO, calcium silicate, barium silicate, and magnesium silicate;

[0020] The particle size of the ceramic powder is 0.5 μm - 30 μm;

[0021] The shape of the ceramic powder is irregular, flaky, spherical, polyhedral, etc.;

[0022] The thermal expansion coefficient of the ceramic powder is (10 - 13) × 10 -6 / K.

[0023] Preferably, the glass transition temperature of the glass powder is 600 - 700 °C, the glass softening temperature is 650 - 750 °C, and the thermal expansion coefficient is (10 - 13) × 10 -6 / K.

[0024] Preferably, the method for preparing the surface polysilazane-modified glass powder comprises: mixing glass powder, polysilazane and a solvent, drying, curing at 250-350°C for 1-4 hours, then heating to 50°C below the glass material transition temperature and holding for 2-6 hours to obtain the surface polysilazane-modified glass powder, with a preferred heating rate of 1-5°C / min; preferably, the solvent is at least one of isododecane, n-hexane, toluene and ethyl acetate.

[0025] Preferably, the method for preparing the surface polysilazane-modified ceramic powder comprises: mixing ceramic powder, polysilazane and a solvent, drying, curing at 250-350°C for 1-4 hours, then heating to below 800-1100°C and holding for 1-4 hours to complete the inorganicization of polysilazane, obtaining the surface polysilazane-modified ceramic powder, with a preferred heating rate of 1-5°C / min;

[0026] Preferably, the solvent is at least one of isododecane, n-hexane, toluene and ethyl acetate.

[0027] Preferably, the thermal expansion coefficient of the high-strength and stable sealant for solid oxide fuel cells is (9-12)×10 -6 / K, the flexural strength > 100 MPa, the thermal conductivity > 1 W / (m·K), and it also has excellent high-temperature stability, being suitable for solid oxide fuel cells.

[0028] In a second aspect, the present invention provides a seal for a solid oxide fuel cell, which is prepared from the above high-strength and stable sealant for solid oxide fuel cells; preferably, the thickness of the seal does not exceed 2 mm, preferably 0.5-1.5 mm;

[0029] In a third aspect, the present invention provides a method for preparing a seal for a solid oxide fuel cell, which comprises:

[0030] (1) Mixing the high-strength and stable sealant for solid oxide fuel cells, a binder, a dispersant and a solvent, passing through screening and vacuum degassing treatments to obtain a printing paste;

[0031] (2) Preparing a green ceramic sheet from the obtained printing paste by tape casting, and then obtaining the seal for the solid oxide fuel cell through cutting, laminating and hot isostatic pressing.

[0032] Preferably, the binder is at least one of cellulose-based and polyvinyl butyral-based, and the addition amount of the binder is 3-7 wt% of the high-strength and stable sealant for solid oxide fuel cells;

[0033] The solvent is at least one of alcohol and xylene, and the addition amount of the solvent is 15-30 wt% of the high-strength and stable sealing material for solid oxide fuel cells;

[0034] The dispersant is at least one of BYK-22552 and fish oil, and the addition amount of the dispersant is 0.5-3 wt% of the high-strength and stable sealing material for solid oxide fuel cells.

[0035] Preferably, the parameters of the tape casting include: the moving speed is 0.2-0.4 m / min, the height of the doctor blade is 100-300 μm, and the temperature is 50-80 °C; preferably, the thickness of the green ceramic sheet obtained is 30-100 μm;

[0036] The pressure of the hot isostatic pressing lamination is 50-60 MPa, the temperature is 70-90 °C, and the pressure holding time is 30-60 minutes.

[0037] Fourthly, the present invention provides a sealing method for a seal for a solid oxide fuel cell, including: placing the seal for a solid oxide fuel cell at the place to be sealed of the solid oxide fuel cell, first degassing at 400-550 °C for 1-3 hours, and then continuing to heat up at a heating rate to 800-950 °C and sintering for 0.5-3 hours to complete the sealing;

[0038] Preferably, the heating rate of the degassing is 0.5-3 °C / min;

[0039] Preferably, the heating rate of the sintering is 1-5 °C / min.

[0040] Fifthly, the present invention provides an application of the high-strength and stable sealing material for solid oxide fuel cells in the fields of aerospace and communication electronics. It can mainly match low-carbon steel, stainless steel, superalloy, etc. used in airtight sealing structures such as metal packaging shells and connectors with a heat resistance of ≥500 °C in the fields of aerospace, communication electronics, etc.

[0041] Sixthly, the present invention provides an application of the seal for a solid oxide fuel cell in the fields of aerospace and communication electronics. It can mainly match low-carbon steel, stainless steel, superalloy, etc. used in airtight sealing structures such as metal packaging shells and connectors with a heat resistance of ≥500 °C in the fields of aerospace, communication electronics, etc.

[0042] Beneficial effects:

[0043] (1) In view of the problems existing in the practical application of composite high-strength sealing materials, such as the chemical interface instability between glass materials and ceramic reinforcement phases at high temperatures for a long time, which leads to phase changes / thermal expansion coefficient changes, etc., resulting in seal failure, the present invention designs a composite sealing material with high mechanical strength and high thermal stability, greatly improving the durability and stability of the sealing material;

[0044] (2) The sealing material of the present invention can also be extended to be applied to airtight sealing structures such as metal packaging shells and connectors with a temperature resistance of ≥500 °C used in the fields of aerospace, communication electronics, etc., made of low-carbon steel, stainless steel, superalloy, etc.;

[0045] (3) There are no toxic components such as Pb, Cr, V, Te, etc. in this glass system, and the preparation process is simple, economical and environmentally friendly. Brief Description of the Drawings

[0046] Figure 1 It is the DSC curve of the glass material used in Examples 1-10 and Comparative Examples 1-2. The glass transition temperature Tg is 640 °C, the initial crystallization temperature Tc is 800 °C, and the two crystallization peaks are at T p1 = 850 and T p2 = 900 °C, indicating that it is a microcrystalline sealing glass material, and ΔT = Tc - Tg = 160 °C, indicating that the glass has excellent thermal stability;

[0047] Figure 2 It is the DSC curve of the glass material used in Examples 11-12. The glass transition temperature Tg is 655 °C, the initial crystallization temperature Tc is 710 °C, and the two crystallization peaks are at T p1 = 755 and T p2 = 860 °C, indicating that it is a microcrystalline sealing glass material, and ΔT = Tc - Tg = 55 °C, indicating that the glass has poor thermal stability and is prone to crystallization;

[0048] Figure 3 It is the TEM image of the modified flaky alumina. It is found from the figure that a protective layer about 5 nm thick can be formed on the ceramic surface after crosslinking curing - high-temperature amorphization;

[0049] Figure 4 They are the XRD patterns of the composite sealing materials in Examples 2-3 and Comparative Example 2 after sealing at 850 °C and then holding at 750 °C for 1 h / 100 h / 1000 h. It is shown by Examples 2 and 3 that the flaky alumina and the high-expansion phase Ba 1.55 Ca 0.45 SiO4 phases can coexist in the initial stage. Although anorthite will appear as the holding time increases, the flaky alumina and the high-expansion phase Ba 1.55 Ca 0.45The SiO4 phase coexists all the time. However, in the unmodified composite material of the comparative example, after 100 h, the high-expansion phase Ca 0.1 Ba 0.9 SiO3 phase reacts to form low-expansion hexagonal and monoclinic feldspar phases and BaAl2O4 phase, resulting in a decrease in the coefficient of thermal expansion, indicating that surface modification can effectively inhibit the chemical stability between the glass phase and the ceramic phase and improve long-term stability;

[0050] Figure 5 FESEM images of the sealing materials of Example 3 and Comparative Example 2 after being kept at 750 °C for 500 h and 1000 h respectively. It is found by comparison that after surface modification, the composite material still has a clear interface after being kept at 750 °C for 1000 h, while in Comparative Example 2, there is still an obvious interface at 500 °C, but after 1000 °C, the flaky alumina has all reacted to form BaAl2O4 phase, indicating that surface modification can effectively inhibit the interfacial reaction between the glass phase and the ceramic phase and improve long-term stability;

[0051] Figure 6 EDS spectrum of the sealing material of Example 3, indicating that the flaky alumina phase remains intact after being kept at 750 °C for 1000 h;

[0052] Figure 7 EDS spectrum of the sealing material of Comparative Example 2. The flaky alumina phase gradually transforms into BaAl2O4 phase after being kept at 750 °C for 1000 h. Detailed implementation mode

[0053] The present invention will be further described below through the following implementation modes. It should be understood that the following implementation modes are only used to illustrate the present invention and do not limit the present invention.

[0054] In the present disclosure, a high-strength and stable sealing material for a solid oxide fuel cell is provided, which is a sealing material composed of a surface-modified glass phase with high expansion and low volatility and oxide powders with different morphologies after surface modification. The surface modification layer can, on the one hand, prevent the volatilization of volatile components (such as B2O3) in the glass, and on the other hand, inhibit the reaction between the glass phase and the alumina phase during long-term operation, so as to improve the mechanical properties (bending strength, elastic modulus, fracture toughness, etc.), thermal stability (high thermal conductivity, high expansion) and chemical stability of the sealing material under long-term operation conditions. Specifically, for the high-strength and stable sealing material for a solid oxide fuel cell, the sealing material combination includes more than 70 wt% of glass powder modified by polysilazane and 5-25 wt% of medium-high expansion ceramic powder modified by polysilazane. The coefficient of thermal expansion of the sealing material combination of the present invention is 9-12×10 -6 / K, the flexural strength > 100 MPa, the thermal conductivity > 1 W / (m*K), and it also has excellent high-temperature stability, is suitable for solid oxide fuel cells, and is also compatible with low-carbon steel, stainless steel, superalloys, etc. used in airtight sealing structures such as metal packaging shells and connectors with a temperature resistance of ≥ 500 °C in the fields of aerospace, communication electronics, etc.

[0055] In an alternative embodiment, the selection of the sealing glass material powder is based on characteristics such as low volatility, high expansion coefficient (10 - 13×10 -6 / °C), being suitable for flat SOFC systems, etc. The components include at least one of the glass network formers B2O3 and SiO2, the B2O3 content is less than 10 mol%, one or more of the network modifiers alkaline earth metal oxides RO (R = Mg / Sr / Ba / Ca) and lanthanide oxides Re2O3, one or more of the network intermediates Al2O3 and Ga2O3, and other components. The sealing material can be either a non-crystallizing glass system or a glass-ceramic system, etc. The preparation method and application of the glass powder in the present invention are as follows: Weigh the raw materials, mix them evenly by ball milling, and then keep them warm in a glass melting furnace at 1450 - 1550 °C for 2 - 4 h; Quench the obtained glass liquid to obtain glass fragments; Then, after washing and drying the glass fragments, ball mill them to obtain glass powder.

[0056] In an alternative embodiment, the medium-high expansion ceramic powder can be at least one of Al2O3, ZrO2, MgO, calcium silicate, barium silicate, and magnesium silicate, and its expansion coefficient is between (7 - 15)×10 -6 / °C. The alumina ceramic powder is amorphous, spherical, octahedral, lamellar, etc. of alumina with a high thermal conductivity.

[0057] In an alternative embodiment, the particle size of the sealing glass material powder is controlled at D50 = 1 - 10 μm. The medium-high expansion ceramic powder is selected from at least one of ZrO2, MgO, calcium silicate, barium silicate, and magnesium silicate with a high expansion coefficient, and the particle size range is between 0.5 - 20 μm. Among them, the flaky powder is a flaky alumina powder with a diameter of 1 - 30 μm and a thickness > 100 nm.

[0058] In the present invention, the glass transition temperature of the glass phase material is 600 - 700 °C, the glass softening temperature is 650 - 750 °C, and the thermal expansion coefficient is (10 - 13)×10 -6 / K. The expansion coefficient of the obtained composite sealing material is (9 - 12)×10 -6 / K, and the working temperature is 700 - 900 °C.

[0059] In an embodiment of the present invention, the specific preparation steps of the composite sealing material are as follows: 1) Prepare the sealing glass material by high-temperature melting - rapid quenching, and control the particle size distribution of the glass powder by rapid ball milling process; 2) Modify the surfaces of the glass powder and the medium-high expansion ceramic material respectively in a certain proportion; 3) Mix the glass powder and the medium-high expansion ceramic material to form a uniformly mixed glass slurry; or cast the uniformly mixed glass slurry or the casting slurry of the glass powder and the medium-high expansion ceramic material in a certain proportion by casting to prepare a green tape of the green body; 4) Cut, cross-stack, hot-press, and cut and shape the composite glass green body; 5) The sintering process during sealing includes a process of degumming - vitrification sealing - crystallization - cooling to the working temperature. This composite sealing material has excellent sealing performance, high-temperature insulation performance, excellent mechanical properties and thermal properties, improves its stability and durability during operation, and the preparation method has a simple process and cheap and green raw materials. The preparation method of the composite sealing material is exemplarily described below.

[0060] Preparation of the sealing glass material. Mixing of the sealing glass phase, high-temperature melting - rapid quenching to form glass, and crushing to obtain glass powder. Specifically, weigh the raw materials according to the formula of the sealing glass material, add a little anhydrous ethanol and mix evenly by planetary ball milling to obtain a mixture. Then melt the mixture at 1450 - 1550 °C for 1 - 4 hours, and finally rapidly cool the melted glass liquid to obtain sealing glass fragments or slag. During the planetary ball milling process, with the mass ratio of zirconia balls: anhydrous ethanol: material being (1 - 3):(2 - 3):(1), ball mill at 100 - 300 revolutions per minute for 6 - 12 h to mix evenly, and dry at 100 - 120 °C. As an example, weigh the Si raw material, B raw material, R raw material, Al raw material, Ln raw material, and other raw materials according to the raw material components of the sealing glass material powder and mix them, then melt at 1450 - 1550 °C for 1 - 4 hours and then rapidly cool to obtain sealing glass fragments. Ball mill the glass fragments or glass slag for 1 - 3 hours to form a uniformly dispersed glass powder, dry, and pass through a 200-mesh sieve. Unless otherwise specified, in the above process of glass preparation, the B raw material is boric acid with a purity greater than 99%. The Sr raw material, Ba raw material, and Ca raw material are one of carbonates and nitrates with a purity greater than 99%. The remaining raw materials are introduced in the form of oxides with a purity greater than 99%.

[0061] In an alternative embodiment, the sealing glass material is planetary ball milled at 300 - 600 revolutions per minute for 1 - 3 hours, passed through a 200-mesh sieve to obtain a uniformly mixed composite sealing material. With the mass ratio of zirconia balls: anhydrous ethanol: material being (2 - 4):(1 - 3):(1). Ball mill the mixed glass fragments at 300 - 600 revolutions per minute for 1 - 3 hours to form glass powder. Then dry at 100 - 120 °C for 6 - 12 h. Then pass through a 200-mesh sieve to obtain glass powder with a particle size of D50 = 1 - 10 μm.

[0062] In an embodiment of the present invention, the glass powder and ceramic powder in the above composite sealing material need to be surface-modified. The preparation processes for modifying the glass powder and ceramic powder are exemplarily described below.

[0063] Preparation of surface-modified sealing glass material. Weigh the glass powder and polysilazane according to the ratio, place them in isododecane and mix evenly to obtain a mixture. Then, evaporate the mixture in a rotary evaporator at 70-100 °C for 10 minutes to 1 hour to obtain glass powder uniformly coated with polysilazane. Then, place the glass powder in a rotary tube furnace, raise the temperature to 250-350 °C and keep it warm for 1-4 h to complete curing, and then raise the temperature to 50 °C below the glass material transition temperature and keep it warm for 2-6 h with a heating rate of 1-5 °C / min to obtain surface-modified glass powder.

[0064] Preparation of surface-modified ceramic material. Weigh the ceramic powder and polysilazane according to the ratio, place them in isododecane and mix evenly to obtain a mixture. Then, evaporate the mixture in a rotary evaporator at 70-100 °C for 10 minutes to 1 hour to obtain ceramic powder uniformly coated with polysilazane. Then, place the glass powder in a rotary tube furnace, raise the temperature to 250-350 °C and keep it warm for 1-4 h to complete curing, and then raise the temperature to below 800-1100 °C and keep it warm for 1-4 h to complete the inorganicization of polysilazane with a heating rate of 1-5 °C / min.

[0065] In the present invention, the modified glass powder, modified ceramic powder, binder, dispersant, plasticizer and organic solvent are mixed together to form a uniform sealing slurry. Alternatively, the modified glass powder, modified ceramic powder, binder, dispersant, plasticizer and organic solvent are mixed together to form a uniform slurry. Then, a green ceramic sheet is formed by tape casting - cutting - laminating - hot isostatic pressing to form a seal. The use process of this sealing material (the use scenario can be sealing or / and connection) includes degassing, nucleation - crystallization process, and achieving sealing. Among them, the degassing regime includes keeping the temperature at 400-550 °C for 1-3 hours.

[0066] The present invention provides a high-strength and stable sealing material, which can also be matched with low-carbon steel, stainless steel, superalloy, etc. used in airtight sealing structures such as metal packaging shells and connectors with a temperature resistance of ≥500°C in the fields of aerospace, communication electronics, etc. In the present invention, a differential thermal analyzer is used to characterize the DSC curve of the glass material. A thermal dilatometer is used to test the thermal expansion coefficient of the obtained glass material and the composite sealing material. A 5566 universal testing machine is used to test the bending strength of the obtained glass material and the composite sealing material. A laser thermal conductivity meter is used to test the thermal conductivity of the obtained glass material and the composite sealing material. A field emission scanning electron microscope and an energy spectrometer are used to characterize the morphology and element distribution of the glass material and the composite material. A transmission electron microscope is used to characterize the coating of polysilazane on ceramic powder and glass powder.

[0067] The following further gives examples to illustrate the present invention in detail. It should also be understood that the following examples are only used to further illustrate the present invention and cannot be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention all fall within the protection scope of the present invention. The specific process parameters and the like in the following examples are also only an example within a suitable range, that is, those skilled in the art can make selections within a suitable range through the description in this article, rather than being limited to the specific values in the following examples.

[0068] Example 1

[0069] According to the glass ratio of Example 1 in Table 1, with a total mass of 2000 grams, calculate and weigh each corresponding raw material: 322.54 grams of SiO2, 180.75 grams of H3BO3, 37.56 grams of Al2O3, 1169.54 grams of BaCO3, 142.18 grams of CaCO3, 69.57 grams of Yb2O3, 52.64 grams of Sm2O3, 18.23 grams of ZrO2, 7 grams of WO3. With the mass ratio of grinding balls: alcohol: raw materials being 2:2:1, ball mill in a nylon tank for 6 hours and then discharge, dry in a constant temperature drying oven at 110°C for 12 hours to obtain a mixture;

[0070] (2) Place the mixture in (1) in a glass melting furnace at a temperature of 1530°C and keep it warm for 3 hours. Use a platinum-rhodium crucible and water-quench the uniformly melted glass melt to obtain glass slag;

[0071] (3) Use the glass slag in (2) with the mass ratio of grinding balls: alcohol: material being 2:1:1, ball mill in a planetary ball mill at 500 revolutions per minute for 2 hours, and dry at 100 - 120°C for 8 hours, and pass through a 200-mesh sieve to obtain glass powder;

[0072] (4) Place 100 g of glass powder and 1 g of polysilazane in 80 ml of isododecane in (3), and perform planetary ball milling at 200 revolutions per minute for 30 minutes. Place the discharged material in a rotary evaporator dryer, and heat it to 90 °C at a speed of 150 r / min until it is completely dried to obtain glass powder uniformly coated with polysilazane;

[0073] (5) Place the glass powder uniformly coated with polysilazane in (4) in a rotary tube furnace, heat it to 300 °C at a heating rate of 2.5 °C per minute and hold for 3 hours, then heat it to 600 °C at a heating rate of 2.5 °C per minute and hold for 3 hours, and then cool it to room temperature with the furnace to obtain modified glass powder;

[0074] (6) Place 100 g of flaky alumina (with a size of 8 - 13 μm in width and 0.5 - 0.7 μm in thickness) and 2 g of polysilazane in 80 ml of isododecane, perform planetary ball milling at 200 revolutions per minute for 30 minutes. Place the discharged material in a rotary evaporator dryer, and heat it to 90 °C at a speed of 150 r / min until it is completely dried to obtain glass powder uniformly coated with polysilazane;

[0075] (7) Place the glass powder uniformly coated with polysilazane in (4) in a rotary tube furnace, heat it to 300 °C at a heating rate of 2.5 °C per minute and hold for 3 hours, then heat it to 900 °C at a heating rate of 2.5 °C per minute and hold for 3 hours, and then cool it to room temperature with the furnace to obtain modified flaky alumina powder;

[0076] (8) First place 90 g of modified glass powder and 10 g of modified flaky alumina (with a size of 8 - 13 μm in width and 0.5 - 0.7 μm in thickness) together with 21 g of alcohol, 21 g of xylene and 2 g of BYK - 22552 dispersant in a nylon pot, perform planetary ball milling at a speed of 400 revolutions per minute for 1 hour, and then add 14 g of PVB 98 binder and 6.8 g of S160 plasticizer and perform planetary ball milling at a speed of 300 revolutions per minute for 1 hour to obtain glass slurry;

[0077] (9) Filter and separate the glass slurry and the grinding balls through a 100 - mesh sieve, and perform vacuum degassing treatment;

[0078] (10) Pour the slurry onto a PCB bottom mold for casting, and let the PCB bottom mold drive it forward at a speed of 0.25 m / min. The thickness of the slurry is controlled at 200 μm by a doctor blade, and the temperature in the casting chamber is controlled at 80 °C. After the slurry is formed into a film strip, remove the bottom mold to obtain a green body (green ceramic sheet). The thickness of the obtained green ceramic sheet is 70 μm;

[0079] (11) Perform simple cutting on the green body, select the number of stacked layers according to the actual use situation, and perform hot isostatic pressing stacking, where the pressure is controlled at 35 MPa, the temperature is 70 °C, and the pressure holding time is 20 minutes;

[0080] (12) Cut the multi-layer green body after hot isostatic pressing into a certain size and shape according to the actual sealing requirements to obtain a seal.

[0081] Example 2

[0082] In this Example 2 (Table 1), the preparation process of the seal refers to Example 1, and the only difference is: 2 wt% polysilazane-modified glass.

[0083] Example 3

[0084] In this Example 3 (Table 1), the preparation process of the seal refers to Example 1, and the only difference is: 80 wt% (2 wt% polysilazane-modified glass) + 20 wt% (2 wt% polysilazane-modified flaky alumina).

[0085] Example 4

[0086] In this Example 4 (Table 1), the preparation process of the seal refers to Example 1, and the only difference is: 80 wt% (2 wt% polysilazane-modified glass) + 20 wt% (4 wt% polysilazane-modified flaky alumina).

[0087] Example 5

[0088] In this Example 5 (Table 2), the preparation process of the seal refers to Example 1, and the only difference is: 80 wt% (2 wt% polysilazane-modified glass) + 10 wt% (4 wt% polysilazane-modified flaky alumina) + 10 wt% (4 wt% polysilazane-modified MgO).

[0089] Example 6

[0090] In this Example 6 (Table 2), the preparation process of the seal refers to Example 1, and the only difference is: 70 wt% (2 wt% polysilazane-modified glass) + 20 wt% (4 wt% polysilazane-modified flaky alumina) + 10 wt% (4 wt% polysilazane-modified MgO).

[0091] Example 7

[0092] In this Example 7 (Table 2), the preparation process of the seal refers to Example 1, and the only difference is: 70 wt% (2 wt% polysilazane-modified glass) + 20 wt% (4 wt% polysilazane-modified flaky alumina) + 10 wt% (4 wt% polysilazane-modified ZrO2).

[0093] Example 8

[0094] In Example 8 (Table 2), the preparation process of the sealant refers to Example 1, with the only difference being: 70 wt% (2 wt% polysilazane-modified glass) + 20 wt% (4 wt% polysilazane-modified flaky alumina) + 10 wt% (4 wt% polysilazane-modified BaSiO3).

[0095] Example 9

[0096] In Example 9 (Table 3), the preparation process of the sealant refers to Example 1, with the only difference being: 70 wt% (2 wt% polysilazane-modified glass) + 20 wt% (4 wt% polysilazane-modified flaky alumina) + 10 wt% (4 wt% polysilazane-modified MgSiO3).

[0097] Example 10

[0098] In Example 10 (Table 3), the preparation process of the sealant refers to Example 1, with the only difference being: 70 wt% (2 wt% polysilazane-modified glass) + 20 wt% (4 wt% polysilazane-modified MgO) + 10 wt% (4 wt% polysilazane-modified MgSiO3).

[0099] Example 11

[0100] According to the glass formulation of Example 11 in Table 3, with a total mass of 2000 grams, calculate and weigh each corresponding raw material: 317.32 grams of SiO2, 185.51 grams of H3BO3, 77.38 grams of Al2O3, 1111.51 grams of BaCO3, 144.658 grams of CaCO3, 102.8 grams of La2O3, 46.48 grams of MgO, 14.34 grams of ZnO. Using a mass ratio of grinding balls: alcohol: raw materials of 2:2:1, ball mill in a nylon jar for 6 hours and then discharge, dry in a constant temperature drying oven at 110°C for 12 hours to obtain a mixture;

[0101] (2) Place the mixture in (1) in a glass melting furnace at a temperature of 1520°C and hold for 3 hours. Use a platinum-rhodium crucible, and water-quench the uniformly melted glass melt to obtain glass fragments;

[0102] (3) Use a mass ratio of grinding balls: alcohol: material of 2:1:1 for the glass fragments in (2), ball mill at 500 revolutions per minute in a planetary ball mill for 2 hours, and dry at 100 - 120°C for 8 hours, and pass through a 200-mesh sieve to obtain glass powder;

[0103] (4) Place 100 g of the glass powder in (3) and 2 g of polysilazane in 80 ml of isododecane, ball mill at 200 revolutions per minute in a planetary ball mill for 30 minutes, discharge and place in a rotary evaporation dryer, heat up to 90°C at a speed of 150 r / min until completely dried to obtain glass powder uniformly coated with polysilazane;

[0104] (5) Place the glass powder uniformly coated with polysilazane in (4) into a rotary tube furnace, heat it at a heating rate of 2.5 °C per minute to 300 °C and hold for 3 hours, then heat it at a heating rate of 2.5 °C per minute to 600 °C and hold for 3 hours, and then cool it to room temperature with the furnace to obtain modified glass powder;

[0105] (6) Place 100 g of flaky alumina (with a size of 8 - 13 μm in width and 0.5 - 0.7 μm in thickness) and 4 g of polysilazane into 80 ml of isododecane, perform planetary ball milling at 200 revolutions per minute for 30 minutes, discharge the material and place it in a rotary evaporator dryer, heat it to 90 °C at a rotation speed of 150 r / min until it is completely dried to obtain glass powder uniformly coated with polysilazane;

[0106] (7) Place the glass powder uniformly coated with polysilazane in (4) into a rotary tube furnace, heat it at a heating rate of 2.5 °C per minute to 300 °C and hold for 3 hours, then heat it at a heating rate of 2.5 °C per minute to 900 °C and hold for 3 hours, and then cool it to room temperature with the furnace to obtain modified flaky alumina powder;

[0107] (8) First place 90 g of modified glass powder and 10 g of modified flaky alumina (with a size of 8 - 13 μm in width and 0.5 - 0.7 μm in thickness) together with 20.5 g of alcohol, 20.5 g of xylene and 2 g of BYK - 22552 dispersant into a nylon pot, perform planetary ball milling at a rotation speed of 400 revolutions per minute for 1 hour, then add 13.5 g of PVB 98 binder and 6.75 g of S160 plasticizer and perform planetary ball milling at a rotation speed of 300 revolutions per minute for 1 hour to obtain glass slurry;

[0108] (9) Filter and separate the glass slurry and grinding balls through a 100 - mesh sieve, and perform vacuum degassing treatment;

[0109] (10) Pour the slurry onto a PCB bottom mold for casting, and let the PCB bottom mold drive it forward at a speed of 0.25 m / min. The thickness of the slurry is controlled at 200 μm by a doctor blade, and the temperature in the casting chamber is controlled at 80 °C. After the slurry is formed into a film strip, remove the bottom mold to obtain a green body (green ceramic sheet). The thickness of the obtained green ceramic sheet is 70 μm;

[0110] (11) Perform simple cutting on the green body, select the number of stacked layers according to the actual usage situation, and perform hot isostatic pressing stacking, where the pressure is controlled at 35 MPa, the temperature is 70 °C, and the pressure holding time is 20 minutes;

[0111] (12) Cut the multi - layer green body after hot isostatic pressing into a certain size and shape according to the actual sealing requirements to obtain a seal;

[0112] Example 12

[0113] In Example 12 (Table 5), the preparation process of the seal was referred to Example 11, with the only difference being: 80 wt% polysilazane-modified glass + 20 wt% polysilazane-modified flaky alumina.

[0114] Example 13

[0115] In Example 13, the preparation process of the seal was referred to Example 3, with the only difference being: 80 wt% (2 wt% polysilazane-modified glass) + 20 wt% (6 wt% polysilazane-modified flaky alumina).

[0116] Example 14

[0117] In Example 14, the preparation process of the seal was referred to Example 3, with the only difference being: 80 wt% (2 wt% polysilazane-modified glass) + 20 wt% (8 wt% polysilazane-modified flaky alumina).

[0118] Example 15

[0119] In Example 15, the preparation process of the seal was referred to Example 3, with the only difference being: 80 wt% (2 wt% polysilazane-modified glass) + 20 wt% (10 wt% polysilazane-modified flaky alumina).

[0120] Example 16

[0121] In Example 16, the preparation process of the seal was referred to Example 3, with the only difference being: 80 wt% (6 wt% polysilazane-modified glass) + 20 wt% (2 wt% polysilazane-modified flaky alumina).

[0122] Comparative Example 1

[0123] In Comparative Example 1, the preparation process of the seal was referred to Example 1, with the only difference being: 100 wt% glass.

[0124] Comparative Example 2

[0125] In Comparative Example 2, the preparation process of the seal was referred to Example 1, with the only difference being: 80 wt% glass + 20 wt% flaky alumina, and neither the glass nor the flaky alumina was modified.

[0126] Comparative Example 3

[0127] In Comparative Example 3, the preparation process of the seal was referred to Example 3, with the only difference being: 80 wt% glass + 20 wt% flaky alumina, and only the flaky alumina was not modified.

[0128] Comparative Example 4

[0129] In Comparative Example 4, the preparation process of the sealant was referred to that of Example 3, with the only difference being: 80 wt% glass + 20 wt% flaky alumina, and only the glass was not modified.

[0130] Table 1 shows the component contents of the composite sealants obtained in Examples 1 - 4:

[0131]

[0132]

[0133] Table 2 shows the component contents of the composite sealants obtained in Examples 5 - 8:

[0134]

[0135]

[0136] Table 3 shows the component contents of the composite sealants obtained in Examples 11 - 12:

[0137]

[0138]

[0139] Table 4 shows the component contents of the composite sealants obtained in Examples 13 - 16:

[0140]

[0141]

[0142] Table 5 shows the component contents of the composite sealants obtained in Comparative Examples 1 - 4:

[0143]

[0144]

[0145] Table 6 shows the mechanical property table of the composite sealants obtained in Examples 1 - 2 and Comparative Example 1 after long - term heat preservation at 750 °C:

[0146]

Claims

1. A high-strength and stable sealing material for a solid oxide fuel cell, characterized in that, Comprising: Surface polysilazane-modified glass powder and surface polysilazane-modified ceramic powder; the content of the surface polysilazane-modified ceramic powder is 10-30 wt%; the content of the surface polysilazane-modified glass powder is 70-90 wt%; the mass of polysilazane in the surface polysilazane-modified ceramic powder is 2-10 wt% of the mass of the ceramic powder; the mass of polysilazane in the surface polysilazane-modified glass powder is 1-4 wt% of the mass of the glass powder; wherein, The preparation method of the surface polysilazane-modified ceramic powder includes: mixing ceramic powder, polysilazane and solvent and drying, first curing at 250-350 °C for 1-4 hours, and then raising the temperature to below 800-1100 °C and holding for 1-4 hours to complete the inorganicization of polysilazane, obtaining the surface polysilazane-modified ceramic powder; The preparation method of the surface polysilazane-modified glass powder includes: mixing glass powder, polysilazane and solvent and drying, first curing at 250-350 °C for 1-4 hours, and then raising the temperature to below 50 °C below the glass material transition temperature and holding for 2-6 hours, obtaining the surface polysilazane-modified glass powder.

2. The high-strength and stable sealing material for solid oxide fuel cells according to claim 1, wherein The mass of polysilazane in the surface polysilazane-modified ceramic powder is 2-8 wt% of the mass of the ceramic powder.

3. The high-strength and stable sealing material for solid oxide fuel cells according to claim 1, characterized in that The composition of the glass powder includes: 25-50 mol% glass network formers, 40-65 mol% glass network modifiers, 2-10 mol% glass network intermediates, 0-5 mol% additives, and the sum of mass percentages is 100 mol%; the particle size D50 of the glass powder is 1 μm-10 μm.

4. The high-strength and stable sealing material for solid oxide fuel cells according to claim 3, characterized in that, The glass network former contains >25 mol% of SiO2 and less than 10 mol% of B2O3; The network modifier contains >30 mol% of alkaline earth metal oxide RO and <5 moL% of rare earth oxide Re2O3, where R = at least one of Mg, Ca, Ba, Sr; The glass network intermediate oxide is Ga2O3 or Al2O3; The additive is at least one of ZnO, Y2O3, ZrO2, iron oxide, cobalt oxide, and nickel oxide.

5. The high-strength and stable sealing material for solid oxide fuel cells according to claim 3, wherein In the alkaline earth metal oxide RO in the network modifier, CaO and SrO are used as regulators for controlling the glass thermal expansion coefficient, and the total content of CaO + SrO is <10 moL%; In the alkaline earth metal oxide RO in the network modifier, BaO and MgO are used as precipitants for controlling the precipitation of high-expansion crystal phases SiO2-BaO phase and SiO2-MgO phase, and the total content of BaO + MgO is ≥30 moL%; 6. The high-strength and stable sealing material for a solid oxide fuel cell according to claim 4, wherein The high-expansion phases precipitated in the glass powder include Ba2SiO4, BaSiO3, BaSi2O5, MgSiO3, Mg2SiO4.

7. The high-strength and stable sealing material for solid oxide fuel cells according to claim 1, characterized in that, The ceramic powder is a ceramic powder with a medium to high expansion coefficient; The particle size of the ceramic powder is 0.5 μm-30 μm; The shape of the ceramic powder is irregular, flaky, spherical or polyhedral; The thermal expansion coefficient of the ceramic powder is (10 - 13)×10 -6 / K.

8. The high-strength and stable sealing material for a solid oxide fuel cell according to claim 7, wherein The ceramic powder with a medium to high coefficient of thermal expansion is selected from at least one of Al2O3, ZrO2, MgO, calcium silicate, barium silicate, and magnesium silicate.

9. The high-strength and stable sealing material for a solid oxide fuel cell according to claim 1, wherein The glass transition temperature of the glass powder is 600 to 700 °C, the glass softening temperature is 650 to 750 °C, and the coefficient of thermal expansion is (10 to 13)×10 -6 / K.

10. The high-strength and stable sealing material for a solid oxide fuel cell according to claim 1, characterized in that In the preparation method of the surface polysilazane-modified glass powder, the heating rate is 1-5 °C / min.

11. The high-strength and stable sealing material for a solid oxide fuel cell according to claim 10, wherein The solvent is at least one of isododecane, n-hexane, toluene, and ethyl acetate.

12. The high-strength and stable sealing material for solid oxide fuel cells according to claim 1, wherein In the preparation method of the surface polysilazane-modified ceramic powder, the heating rate is 1-5 °C / min.

13. The high-strength and stable sealing material for solid oxide fuel cells according to claim 12, wherein The solvent is at least one of isododecane, n-hexane, toluene, and ethyl acetate.

14. A seal for a solid oxide fuel cell, characterized in that, It is prepared from the high-strength and stable sealing material for solid oxide fuel cells according to any one of claims 1-13.

15. The seal for a solid oxide fuel cell according to claim 14, characterized in that, The thickness of the seal is not more than 2 mm.

16. The seal for a solid oxide fuel cell according to claim 14, characterized in that, The thickness of the seal is 0.5-1.5 mm.

17. A preparation method of a seal for a solid oxide fuel cell as described in claim 14, characterized in that, It includes: (1) Mix the high-strength and stable sealing material for solid oxide fuel cells, binder, dispersant, and solvent, and after sieving and vacuum degassing, obtain a printing paste; (2) Cast the obtained printing paste to form a green ceramic sheet, and then through cutting, laminating, and hot isostatic pressing, obtain a seal for solid oxide fuel cells.

18. The preparation method according to claim 17, wherein The binder is at least one of cellulose derivatives and polyvinyl butyral, and the addition amount of the binder is 3-7 wt% of the high-strength and stable sealing material for solid oxide fuel cells; The solvent is at least one of alcohol and xylene, and the addition amount of the solvent is 15-30 wt% of the high-strength and stable sealing material for solid oxide fuel cells; The dispersant is at least one of BYK-22552 and fish oil, and the addition amount of the dispersant is 0.5-3 wt% of the high-strength and stable sealing material for solid oxide fuel cells.

19. The preparation method according to claim 17, characterized in that, The parameters of the casting include: the moving speed is 0.2-0.4 m / min, the height of the doctor blade is 100-300 μm, and the temperature is 50-80 °C; The pressure of the hot isostatic pressing is 50-60 MPa, the temperature is 70-90 °C, and the holding time is 30-60 minutes.

20. The preparation method according to claim 19, wherein The thickness of the obtained green ceramic sheet is 30-100 μm.

21. A sealing method for the seal of the solid oxide fuel cell according to claim 14, characterized in that, It includes: Place the seal for solid oxide fuel cells at the location to be sealed of the solid oxide fuel cell, first heat it at a heating rate to 400-550 °C for 1-3 hours to remove plasticizers, and then continue to heat it at a heating rate to 800-950 °C for 0.5-3 hours to complete the sealing.

22. The sealing method according to claim 21, wherein, The heating rate for removing plasticizers is 0.5-3 °C / min.

23. The sealing method according to claim 21, characterized in that, The heating rate for sintering is 1-5 °C / min.

24. Application of the high-strength and stable sealing material for solid oxide fuel cells according to any one of claims 1-13 in the fields of aerospace and communication electronics.

25. Application of the seal for solid oxide fuel cells according to claim 14 in the fields of aerospace and communication electronics.

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